I'm having serious problems with upgrading dev-libs/icu-50_rc-r1:0/50 which makes my machine unusable until I downgrade to icu-49.1.2:0
I keep getting errors about missing libicuuc.so.49 but I'm not sure what package is dependant on the older version. I can't even start KDE until I downgrade, I tried revdep-rebuild but it didn't help.
Is anyone else experiencing this or have an idea how to fix it?

My first hour was in vain with having only icu-50_rc-r2
But the incoming icu -r3 revision saved my day!
I managed to do a full emerge -e @system without errors then.
I have a 64 bit Gentoo system with unstable~current keyword ~amd64.
Now I am recompiling @world ..._________________fun2gen2

Nice one ulenrich. I think I might add an ABI warning for this lot to update.

Would it be correct to warn on any of:
>=dev-libs/boost-1.50
>=dev-libs/icu-50
>=sys-devel/gcc-4.7
>=sys-libs/glibc-2.16
and then do the qlist thing? (We have that check builtin already, so I can just give it the parameters you did.)

I'm guessing all of those need to be above the versions above, to work together correctly?

It is masked for a reason:
1. At a previous icu revision stage I could compile libreoffice but not chromium.
2. Today I can compile chromium but not libreoffice And the two days old libreoffice cannot start anymore.

With gcc-4.7.2 there is the implementation of new general c++ standard. Previous gcc versions had their own GNU-c++. To have ABI compatibility across our Gentoo distribution all is turned back to GNU-c++ for the time being._________________fun2gen2

Excuse my ignorance but what do I need to do to fix this?
After downgrading back to icu-49.1.2 I can't seem to either revdep-rebuild or update anything without problems.
Here's what versions I'm running, I'm using ~x86_64. I can't seem to upgrade KDE to 4.9.3 hence my other post

and I suspect this is due to the icu update/downgrade and I can't revdep-rebuild because most of the packages fail as well. I get openldap-4.9.3 failing to build along gnutls errors, samba fails because of openldap and so it goes on.

@andrewwalker27,
you normally get through by sticking to a single Gentoo release of the two (amd64 or ~amd64).
As you are at Gentoo~current there may be short times difficulties when transitions occur:
So I don't know what about boost-1.52 and boost-build-1.52 at this moment. (Because I am running all of these unreleased and masked packages at the moment.) You would surely get through by stibilizing to boost-1.49.0~r2 as long as you stick to gcc-4.6.3 and icu-49.1.2.